Heretofore, the prior art has proposed the use of various electrical switching means and structures whereby, for example, the vehicle operator manually actuated such switching means to an electrically closed condition to thereby supply electrical current to the vehicular window heaters and, subsequently, upon some indeterminate span of time, the vehicle operator would manually actuate such closed switching means to an electrically open condition to thereby terminate electrical current to the window heaters. Such manual control often resulted in the operator forgetting to open the switching means thereby resulting in an attendant excessive current drain as on the vehicular battery.
In an attempt to overcome this problem, the prior art has proposed the employment of various timing circuits to be employed, in effect, in combination with the switching means in order to thereby limit the total time, as per any one occurrence of switch means closure, to a preselected maximum span of time. Such prior art devices have not been found acceptable for various reasons among which are that such prior art timing means usually exhibited variable time spans, instead of a substantially constant time span as desired and they are very sensitive to temperature and as a consequence thereof any one prior art timing means often exhibited variations in its timing function with such variations being temperature induced. Further, such prior art devices are usually quite complex requiring many electrical connections and other special considerations as in the installation thereof within an automotive vehicle. For example, some prior art systems proposed the use of physically separate circuitry which in turn had to be connected as by plug-in type terminals to related timing circuit means and to remotely situated manually actuated switching means and the circuitry then, in turn, also had to be connected as by electrical harness means to a source of electrical potential and to the vehicular backlight heater means.
Accordingly, the invention as herein disclosed, described and claimed is primarily directed to the solution of the foregoing and other related and attendant problems of the prior art.